VLCTY

I just purchased a set of OE Cup wheels for my 2007 Z. I want to wrap them in Michelin Super Sports but I'd like to go with a wider and taller tire on the rear, compared to the OE tire spec of 285/30/19 & 335/25/20. If I mounted 345/30/20's on the rear and 285/35/19's on the front, would this tire size ratio match the OE spec and eliminate any possible issues with ABS or Traction Control? Also, are there any reasons why I shouldn't change the tire sizes from the OE spec? Any advice would be appreciated!

Mordeth

You have to maintain a ratio of diameter of 1.04 between rear and front. That is, the rear wheel + tire diameter is 1.04 times bigger than the front rear + tire diameter. (technically it is 1.0466 but we will round to 1.04). So let's figure it out.

Front tires: Tire is 285mm wide. Aspect ratio is 30%. So the sidewall is 85.5mm high. The wheel is 19in diameter. Converted to 482.6mm. So we add both sidewalls to the wheel diameter to get the total diameter of tire plus wheel. 85.5 + 85.5 + 482.6 = 653.6mm

Rear tires: Tire is 335mm wide. Aspect ratio is 25%. So the sidewall is 83.75mm high. The wheel is 20in diameter. That is 508mm. Add both sidewall heights to the wheel diameter. 83.75 + 83.75 + 508 = 675.5mm . This is the total diameter of a rear wheel + tire.

So 675.5/653.6 = 1.033 ratio. That is slightly lower than the OE spec. I am thinking you won't have TC/AH issues as you are pretty close, but no guarantee. I think most have problems when the ratio is closer to 1.0 or 1.01.